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<h1 id="dc--operating-point-analysis">DC / Operating point analysis</h1>

<h2 id="operating-point-calculations">Operating point calculations</h2>
<p>The operating point of a circuit is the static solution to a a circuit, ie. all voltages and currents are assumed to be constant over time.</p>
<p align="center"><img src="images/operatingpoint.svg"></p>
<p>Calculating the operating point is often the first step in any simulation. First the temperature-dependent properties are calculated. Then the analysis will <strong><a href="iterate.html">iterate</a></strong> to find a solution. Iterative solutions do not always guarantee convergence, so multiple schemes are provided to help convergence if the first attempt fails.</p>
<h2 id="gmin-stepping">Gmin stepping</h2>
<p>A common issue for convergence is exponential dependencies of a current on a voltage or vice-versa, like is often the case in diode-type structures (PN-junctions). The problem occurs because on one side of the exponential the curve is very horizontal, while on the other side it is almost vertical. This causes iterations to either over-step, or under-step when the current solution is too far from the real solution. By placing an additional resistive path in parallel to these problematic areas this issue can be alleviated. Usually a high <strong>Gmin</strong> allows the circuit to converge pretty quickly to a solution that is closer to the actual solution. This new solution can be used to iterate again with progressively smaller <strong>Gmin</strong> as the solution gets closer and closer to the actual solution.</p>
<h2 id="diagonal-gmin-stepping">Diagonal Gmin stepping</h2>
<p>Diagonal Gmin stepping is almost identical to Gmin stepping, except that it will add a resistor to <strong>ground</strong> from each node in the circuit, not just for exponential curves. This translates to adding <strong>Gmin</strong> to each diagonal element of a voltage node in the Y-matrix - hence the name.</p>
<h2 id="source-stepping">Source stepping</h2>
<p>For source stepping, all independent sources are given a value of 0 volts or 0 amps. The solution should at that point be trivial (all voltages and currents will be very close to 0). By slowly ramping up all independent sources again, a solution can be found where the solution does not change as much from one step to the next.</p>
<h1 id="dc-analysis">DC analysis</h1>
<p>A DC analysis is nothing more than a sequence of operating point analysis where one or more parameters are being swept.</p>
<p>Temperature-dependent calculations are executed only once at the start of the sweep.</p>

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